A fascinating study in Health Affairs last year by a father-daughter pair of public policy researchers found that Medicare prescriptions for things like painkillers, antidepressants and anti-anxiety medications dropped sharply in states that introduced a medical marijuana program.

The implication? Offered the choice between taking medication prescribed by a doctor and self-medicating with pot, many older patients opted for the latter.

But the study left one big question unanswered: Since the study’s authors — the University of Georgia’s Ashley Bradfordand W. David Bradford — only looked at Medicare data, they couldn’t say for sure whether the findings held for younger patients too.

Now, we’re getting more answers. This week, the Bradfords are back with a new study applying the same analysis to prescriptions under Medicaid, which covers low-income people of all ages. The results largely validate their previous work: Medicaid prescriptions for certain drugs fell significantly in states that adopted a medical marijuana law.

Not everyone who has access to medical marijuana opts for it, obviously. But enough do to make a significant dent in the prescription numbers. “Patients and physicians in the community are reacting to the availability of medical marijuana as if it were medicine,” the Bradfords conclude.

Perhaps most significantly from a public health standpoint, prescriptions for painkillers fell by 11 percent. Opiate painkillers are behind much of the current drug overdose epidemic.

Numerous studies have found that opiate abuse and overdose rates fell in states with medical marijuana laws. The Bradfords’ research describes the mechanism by which that could happen: the introduction of medical marijuana laws coincides with a drop in painkiller prescriptions.

The Bradfords’ data only include prescriptions made under Medicare and Medicaid, but given the totality of their evidence it seems reasonable to assume that similar patterns hold true for patients on private insurance plans.